LTC4360ISC8-2TRMPBF datasheet(9/12 Pages) LINER

9 / 12 page

LTC4360-1/LTC4360-2

436012f

APPLICATIONS INFORMATION

Figure 6. 50V Hot-Plug into the LTC4360

Figure 7. Input Transient After Overvoltage

VIN

20V/DIV

VOUT

1V/DIV

ICABLE

5A/DIV

5μs/DIV

436012 F05

FDC5612

RIN = 150mΩ, LIN = 0.7μH

LOAD = 10Ω, COUT = 10μF

VADAPTOR/VOUT

5V/DIV

VIN

20V/DIV

ICABLE

5A/DIV

2μs/DIV

436012 F06

FIGURE 5 CIRCUIT

RIN = 150μΩ, LIN = 2μH

LOAD = 10Ω, COUT = 10μF

VADAPTOR

VOUT

As the IN pin can withstand up to 80V, a high voltage N-

channel MOSFET can be used to protect the system against

rugged abuse from high transient or DC voltages up to the

BVDSS of the MOSFET. Figure 6 shows a 50V input plugged

into the LTC4360 controlling a 60V rated MOSFET.

Input transients also occur when the current through the

cable inductance changes abruptly. This can happen when

the LTC4360 turns off the N-channel MOSFET rapidly in an

overvoltage event. Figure 7 shows the effects of a voltage

transient at the wall adaptor output VADAPTOR. The cur-

rent in LIN will cause VIN to overshoot and avalanche the

N-channel MOSFET to COUT. Typically, IN will be clamped

to a voltage of VOUT + 1.3•(BVDSS of Si1470DH) = 45V.

Figure 5. 20V Hot-Plug into the LTC4360

LOAD

LTC4360

Si1470DH

GND

GATE

436012 F04a

MOBILE

DEVICE

WALL ADAPTOR

AC/DC

COUT

OUT

LIN

RIN

CABLE

ICABLE

OUT

VIN

10V/DIV

VOUT

1V/DIV

ICABLE

20A/DIV

5μs/DIV

436012 F04b

RIN = 150mΩ, LIN = 0.7μH

LOAD = 10Ω, COUT = 10μF

This is well below the 85V absolute maximum voltage

rating of the LTC4360. The single, nonrepetitive, pulse of

energy (EAS) absorbed by the MOSFET during this ava-

lanche breakdown with a peak current IAS is approximated

by the formula:

EAS = 0.5 • LIN • IAS2

For LIN = 2μH and IAS = 4A, then EAS = 16μJ. This is within

the IAS and EAS capabilities of most MOSFET’s including

the Si1470DH. So in most instances, the LTC4360 can

ride through such transients without a bypass capacitor,

transient voltage suppressor or other external components

at IN.

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